Leaf scorching due to foliar application of synthetic acid mine drainage and the effectiveness of an antitranspirant in protecting leaves

Abstract

Untreated acid mine drainage (AMD) is being considered for crop irrigation on strategically limed soils, but foliar scorching is of potential concern. To test whether crops might be protected by antitranspirants, a field trial and two glasshouse pot trials were undertaken during the 2020/2021 growing seasons. Crops, namely Sorghum bicolor, Zea mays, Glycine max, Vigna unguiculata, Triticum aestivum, Avena sativa, Medicago sativa, and Pisum sativum, were exposed to acid water with pH levels of 2.0, 2.5, 3.0, 4.0, and 7.0. The first pot trial and field trial tested the effects of sulphuric acid solutions (to simulate AMD) on leaf scorching and the second pot trial focused on the effectiveness of an antitranspirant, Wiltpruf®, in protecting crops against leaf scorching. Leaf scorching occurred at pH levels of 2.0, 2.5, and 3, but only to a maximum of 6% leaf area damage in the worst-affected crop species. Crops are likely to recover from this injury. Contrary to expectations, the antitranspirant increased the propensity for foliar injury among crops, especially at pH 2.0 and 2.5. Metal cations commonly found in AMD should be included in follow-up leaf scorching studies to better simulate likely AMD irrigation waters. However, it appears that any crop growth problems possibly encountered when irrigating with AMD are likely to stem from root zone effects.